Hi I moved to Sydney when dd ws around 3 in 2009 so know it well. we back in uk right now but I went last april for a month with dd (then 8) and my parents.
This was my 30th bday present from them and although 1 extra adult I do think you may be setting your price far too low.
Not including flights (we went emirates business class using air mile upgrades) the total trip cost approx. 20 grand GBP!
We flew from Dubai (parents live there so I stopped off for few days and then we all went together) into Perth.
We did stay at high end places and we did eat out every day for breakfast, lunch and dinner again as high end places and we hired car and did trips. Our itinerary is below.
4 nights in Perth saying with friends.
Drove to Margaret River (wine tasting country) and spent 3 nights there.
Drove back to Perth and stayed 1 night.
Flew to cairns and picked up Car at airport and drove up To Port Douglas for 4 night ( most beautiful place in Australia I have ever been and I have been most places)
Did all the daintree rainforest trips and train and cable car, went scuba diving etc
Droveback down through cairns which we had done previously so went on through and stopped in Townsville (not nice place) for the night.
Drove to Airlee beach which was amazing and stayed for 3 nights, did all the usual island trips
Then we drove to Hervey bay and stayed 2 nights, did Fraser Island Tour Etc
Drove down to the Gold coast staying few nights along the way at places, and stayed 5 nights finally in the Gold coast. We always stay right on a place called Teder Avenue which has the most amazing strip of resturants and hotels, is expensive but wrth it!!!!
We also did Tribulation island, the Australia zoo, crocodile tours, cave tours etc etc.
Was great holiday and cant wait to move back very soon.
Have fun and enjoy!